Process of preparing methyl alpha-methyl-beta-mercaptopropionate



Patented Dec. 30, 1941 UNITED STATES PATENT F rnocsss or rnarmino MaruYL-nmA-Msncmornoniom'rr:

This invention relates particularly, to a process of preparing methyl alpha-methyl-beta-mercaptopropionate.

An object is the preparation of new petroleum chemicals, pesticides. and intermediates for other chemical products. Other objects will appear hereinafter.

These objects are accomplished-by the following invention wherein a monomeric ester of an aipha,beta-unsaturated monocarboxylic acid and preferably of an alpha methylene aliphatic monocarboxylic acid is reacted with hydrogen sulfide preferably in the presence of a basic catalyst, e. g. an amine. The products which are new and useful compositions of matter are derivatives of hydrogen sulfide and are esters of monomeric monocarboxylic acids having a mercapto (SH) group on the beta carbon atom and at least one hydrogen on the alpha carbon atom.

In a generally preferred mode of executing the process of the present invention. the ester of the alphabets-unsaturated acid, hydrogen sulfide, and a catalyst such as piperidine are placed in a pressure vessel, cooled in a suitable bath, e. -g., an acetone-solid carbon dioxide bath. After the pressure vessel is sealed, it is heated at 75-180 C.

for twelve to twenty-four hours, then cooled and opened. The components of the crude reaction product are separated by fractional distillation under reduced pressure.

The more detailed practice of the invention is illustrated by the following examples, wherein parts given are by weight. There are of course many forms of the invention other than these specific embodiments.

EXAMPLE I MET Yl. 22-11mmYL-3-liiER0AP'roPRoi-ioNATE Twenty-four and five-tenths (24.5) parts of methyl a-methacrylate (0.245 mole) and twelve (12) parts of hydrogen sulfide (0.35 mole) are placed in a steel bomb cooled in an acetone-solid carbon dioxide bath. The closed vessel is heated for twelve hours at 200 C.. after which it is cooled and opened and the resulting mixture is then distilled. Four (4) parts of methyl 2- methyl-3-mercaptopropionate HSCH2CH(CH3) COOCHa B. P. 6'l-69 C./32 mm. containing 23.05% S. the theoretical amount being 23.88% is obtained.

EXAMPLE II Mlri'nri. Q-AIETHYL-3-1IERCAPTOIROPIONATE Forty (40) parts of methyl a-methacrylate (0.4 mole). seventeen (17) parts of hydrogen sulflde (0.5 mole). and one (1) part of piperidine are added we pressuretube cooled in an acetonesolid carbon dioxide bath. The tube is sealed and heated for twelve hours at C.. and is then cooled and opened. Upon distillation of the resultingmixture, twenty-nine (29) parts of methyl 2-methyl-3 mercaptopropionate, B. P. 58-60 C./10 mm.. is obtained.

EXAMPLE III Burn. 2-.imam-3 1M211ProrRorIoNA'i-s In a pressure reactor cooled in an acetonesolid carbon dioxide bath are placed forty-two and six-tenths (42.6) parts of n-butyl-a-methacrylate 0.3 mole). seventeen (17) parts of hydrogen sulfide (0.5 mole) and one (1) part of piperidin'e. The reactor is closed and then heated for twelve hours at 90 C. After cooling. the reaction vessel is opened. the contents distilled, and

3-mercaptopropionate, HSCH2CH(CH3) COOC4H9 containing 17.36% S, the theoretical content being 18.18%.

1 EXAMPLE IV "(oroxl'T ALCUHULS" ESTERS OF 2-lilnTI-IYL-3-MER- (APTOIROPIONIC ACID Forty-six (46) parts of the a-methacrylate of "coconut alcohols," i. e. the mixture of monohydrlc alcohols obtained by hydrogenation of coconut oil or oil acids, ten and six-tenths (10.6) parts of hydrogen sulfide, and one 1) part of piperidine are placed in a steel bomb tube cooled in an acetone-solid carbon dioxide bath. The tube is then closed and heated for twelve hours at 160 C. The tube is cooled and opened, and the product is removed and fractionally distilled. The fraction boiling at -156 C. is the coconut alcohols esters of 2-methyl-3-m'ercaptopropionic acid: it contains 10.25% sulfur, the theoretical content being 11.1%.

While in the process of the present invention, the temperature may range from that at which the reaction begins to be detectableabout 25 C. in the presence of, and about 95 C. in the abwherein the process is applied to monomeric sence of, a catalyst-up to the decomposition monohydric alcohol esters of alpha-methylene, temperature of the products, i. e. about 300 C. open chain aliphatic monocarboxylic acids, 1. e.,

or even higher, and the pressure may be atmosopen chain aliphatic monocarboxylic acids in pheric, the results at the lower temperature exwhich a CH2 group is attached to the alpha cartremes and atxatmdspheric pressure are. not enbon atom by an et yle ic double bOnd the recouraging for "any commercially feasible process. "sultant products are monomeric monohydric alco- Best results are obtained at 75-180" C. in a closed hol esters of alpha-mercaptomethyl aliphatic system under superatmospheric pressure in the monocarboxylic acids having, in addition to the presence of a catalyst. Thus Example I above,: 10 -mercaptomethy1 group at least one hydrogen on although employing a temperature of 200 C., thea lpha carbon atom. Similarly, when metha- Gil shows a yield of only 12% mercaptan whereas crylic acid esters are used, the products are Example 11 which utilizes a catalyst shows a esters of 'alphamercaptomethyl propionic acid yield of 54% mercaptan at a reaction tempera having a hydrogen atom, a methyl group and a ture of 90 C. Operation with a catalyst allows l5nmercaptomethylv group on the carbon alpha to the use of lower temperatures. the esterified carboxyl group.

While the examples disclose piperidine as the Additional esters of a, p-unsaturated monocatalyst, any basic compound stable at reaction carboxylic acids, and the products obtainable temperature may be used including basic or-v from them by the process of the present inven-' ganic compounds in general, e. g. butylamine, tion are listed in the table below:

Table I Ester Mercaptan Met yl acrylate Propyl acrylate OH1=CHCOOC3H1 Ethyl cinnamate Cyclohexyl methaorylate CH1=C (OHQCO OCtHu B-Chloroethyl methacrylate OH= (CH3) COOCHzCHzCl Scc-butyl methacrylate s Ter-butyl methacrylate CHz= 0 (CH3) COOC(CH3)1 Ethyl crotonate Phenyl methacrylate CH:=O(GH3)COOC@H Methyl-3-mercaptcpropionate. HSCHzCHxCOOCHI Propyl 3-mercaptopropionate.- HSCHnCH1COOCIH1 Ethyl 3-mercapto-3 henylpro'pionatc. CH5CH(SH)C :COOCzHs Cyclohexyl Z-methyl-3-mercargopropionate.

HSCH:CH(CH3)COOC! n B-Hydroxyethyl 2-methyl-3-mercaptopropionatc.

fl-Chloroethyl Z-methyl-amergaptoprofionate.

HSCHzCHi(CHa)COOCH2CH1C Sec-butyl 2-methyl-3-mermstopropionate. HSCH:CH(CH;)COO H(CH;)C,H;

Ter-butyl 2-methyl-3-merca topropionatc.

HSCHaCH(CHa)COO (CH3):

Ethyl 3-mercaptobutyrate.

CHaCH(SH)CHiOO0C1Hs B-Ethoxyethyl Z-methyI-Bmerca topro innate. HSCHCH(CH1)COOCH: H H.

Methyl alpha-ethylacrylate Methyl 2-ethyl-3-mercaptopro ionate.

om=cwmnooocm nscrncmcinocooc 1 Methyl alpha-heptylacrylate Methyl 2-heptyl-3-mercaptopropionate.

OH1=C(G1Hn)COOCHa nsomcmcmmooocm Methyl alpha-phenylacrylate Methyl 2- henyl-3-mercaptopropionatc.

CH1=C(CQH5)COOCH3 HSO icmotngcoocn, Methyl tiglate M thyl Z-methyl-S-mereaptobutyrate.

CH3CH=O OH9COOCH3 omomsmcmcnocooom Methyl dimethylcrotonate Methyl 2 3-dimethyl-3-mercaptobutyrate. om)lo=c cm)oooom (cmbmsmomonocooom diethylamine, ethanolamine, morpholine, aniline, The mercaptans of the present invention have triethylamine, cyclohexylamine, phenyl hydrathe formula: zine, tetramethylammonium hydroxide, sodium so t 0 acetate, and sodium methylate, as well as basic ll inorganic compounds, e. g., sodium hydroxide, sodium carbonate, calcium oxide and ammonia. H

The process is not limited to the ratio of rewherein R is the radical of an organic hydroxyl actants disclosed in the examples given. An compound, 1. e. an alcohol or phenol minus at excess of hydrogen sulfide beyond the 1:1 molar least one of its hydroxyl groups and a: is the numratio increases the yield of the mercapto derivaber f th missing hydroxyl groups, R may b tive.' I saturated or unsaturated, monovalent or poly- While the illustrative examples show variations valent, aliphatic, aromatic, alicyclic' or hetero-,- in t Process as ppl d to the preparation of 0 cyclic, but is usually aliphatic and is preferably beta-carboalkoxypropyl derivatives of H--SH monovalent. The corresponding alcohols and by the interaction of the methyl, butyl, and the phenols are, for example, methanol, cyclohexanol,

"coconut alcohols" esters of methacrylic acid benzyl alcohol, ethoxyethanol, dodecanol-l, beta- .wlth hydrogen sulfide, it is of generic appH- chloroethanol, sec. butanol, phenol, naphthol,

cabi ityto a y m0n0meri0,pre1erab1y monohydric furfuryl alcohol, glycol, glycerol, xylenol.

alcohol, ester of an alpha-beta-unsaturated When R is monovalent, i. e. when the alcohol monocarboxylic, preferably aliphatic monocaris monohydric, or it polyhydric is only esterifled bo y d- The products of the'invention may with one mol of acid the formula reduces to be described as, and the invention is generic to,

esters, preferably monohydric alcohol esters, of R E n monomeric monocarboxylic, preferably aliphatic,

acids having a mercapto (SH) group on the beta R H carbon and at least one hydrogen on the alpha wherein R R and R have the same values as carbon. before, i. e., may each be hydrogen or a mono- In the preferred modification of the invention. valent, saturated or unsaturated, substituted or unsubstituted, aliphatic, aromatic, alicyclic, or heterocyclic organic radical, for example, methyl, benzyl, allyl, dodecyl, cyclohexyl, phenyl, betahydroxyethyl, beta-chloroethyl, sec. butyl, betaethoxyethyl, etc.

The new esters of hydrogen sulfide prepared as described herein may be used as petroleum chemicals, pesticides, agents for controlling the emulsion polymerization of chioroprene, and as intermediates in the preparation of other compounds.

The process of preparing thepresent derivatives of hydrogen sulfide by the interaction of hydrogen sulfide and alpha,beta-unsaturated esters is a one-step process which may be readily carried out. The products may be obtained in good yields and may be readily isolated by fractional distillation. The reaction may be carried out under a wide variety 01' conditions of temperatures, pressure, and concentration of reactants. These variables may be adjusted for each particular alpha,beta-unsaturated ester to obtain the optimum yield 01' the mercaptan. As shown above, this process is applicable to a wide variety of alpha,beta-unsaturated esters.

The above description and examples are intended to be illustrative only. Any modification of or variation therefrom which conforms to the spirit of the invention is intended to be included within the scope of the claim.

We claim:

Process of preparing methyl alpha-methylbeta-mercaptopropionate which comprises putting approximately one and one-half mols of hydrogen sulfide with one mol of monomeric methyl methacrylate in an autoclave, heating at 200 C. under superatmospheric pressure, and isolating the methyl alpha-methyl-beta-mercaptopropionate.

WILLIAM JAMES BURKE. FRANKLIN TRAVISS PETERS. 

